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...what is the point of having such high resolution in a camera (not necessarily the 7D, but any camera) if the resolution cannot be fully used to make prints? If the only way a particular camera looks good is when the images are drastically subsampled, then you have paid for sensor resolution that you can't really utilize.
That's not it at all; the correct way to compare cameras if one makes prints is to compare prints. If you print an 18MP image at 8X10 and an 8MP image at 8X10 (or whatever given size, as long as they're equal) you will have a true comparison. Looking at 100 pixels from each on screen will not give an accurate comparison. Because each pixel prints smaller when you have more pixels on the same size print, noise will be smoother and less visible.
You can do the same on screen, by comparing each camera's images at the same screen size, but not at 100% because you wll be artifically increasing the size of the noise from the higher-resolution camera. Think about it: when sending your pictures to be viewed by others, would you send only a certain number of pixels from part of the image, or would you send the whole image? I'd send the whole image, and whether it was taken with my 8MP 20D or my 18MP 7D I'd expect the viewer to look at the whole image at once, sized to take up most if not all of his or her monitor's real estate.